In a food industry field, it is necessary to confirm that food products of which the number of microorganisms needs to be counted do not cause problems, or that useful microorganisms are properly grown in the food manufacturing process. As a viable cell detection system used for this confirmation, cultivation-type counting means using a culture medium is often used. For example, there has been used a method of counting the number of microbial colonies using an agar medium as an official method of counting microorganisms. In particular, for counting target products having a low distribution of microorganisms, the above method has been widely used as means by which microorganisms are cultivated in a short time period to develop microbial colonies and the number of microorganisms is counted in an easy and simple manner with a good accuracy.
Alternatively, instead of a conventional method of visually counting the number of colonies developed in an agar medium or the like, there have been proposed several methods of automatically counting the number of colonies by performing data processing on the image of a counting target culture medium taken by a CCD camera or the like. That is, the proposed colony counting methods include a method of counting the number of colonies by identifying the connected colonies by the shape (see Patent Document 1) and a method of counting the number of microorganisms by detecting an peripheral arc of colonial microorganisms using shading of hues (see Patent Document 2).
Further, there has been proposed a method of counting the number of colonies with a good accuracy by performing data processing on a CCD camera image using hues in an easy and simple manner (see Patent Document 3). The present applicant has proposed an inspection method of automatically counting the number of colonies with a good accuracy using a monochrome CCD camera by dividing the colony inspection regions (see Patent Document 4).
However, it has been apparent from past experience that conventional colony counting means provides a different number of colonies for each counting when the number of colonies in the same counting target petri dish is counted if the lighting plan position and the lighting angle with respect to the target petri dish and the distance between the CCD camera and the petri dish and the like are changed. The reason is mainly that colony image data taken by the CCD camera is changed because of the complicate relationship of the relative position of the lighting and the CCD camera and the relative position of the colonies with respect to minute colonies developed and scattered in various depth ranges in agar media and the like, resulting in a variation of automatic colony count in conjunction with data processing method for the image data.
For this reason, the food industry required to have an accurate number of colonies has been seeking a practical colony counting method that ensures stable counting data by eliminating the variations of the number of colonies in the same petri dish.
Patent Document 1: Japanese Laid-Open Patent Publication No. H09-140397
Patent Document 2: Japanese Laid-Open Patent Publication No. 2001-22929
Patent Document 3: Japanese Laid-Open Patent Publication No. 2004-194610
Patent Document 4: Japanese Laid-Open Patent Publication No. 2006-345750